This invention relates to fungi which produce D-glucose oxidase, methods of obtaining such fungi and the use of such fungi to obtain oxidase.
It is known to utilize fungi to produce oxidase. Moreover, it is known to select mutants that produce increased proportions of enzymes from cultures of wild type fungi.
One prior art fungus producing D-glucose oxidase as an adaptive or induced enzyme is the wild type fungus Aspergillus niger. This fungus and a method of obtaining D-glucose oxidase are described in U.S. Pat. No. 3,102,081. The prior art wild type Aspergillus niger is not as suitable for producing D-glucose as desired under current demand conditions for D-glucose because: (1) it produces substantially larger amounts of gluconate constituitively and a smaller amount of D-glucose oxidase when induced, whereas demand conditions now favor a higher proportion of D-glucose oxidase and the market for D-glucose oxidase is growing faster than for gluconate; and (2) the wild type Aspergillus niger requires a large amount such as 0.5M glucose to induce the production of D-glucose oxidase.
It has been proposed to obtain mutants of Aspergillus niger that produce a higher yield of D-oxidase. One known method for selecting mutants of a fungus, which mutants have a higher production of the enzyme than a wild-type fungus includes exposing the wild type fungus to a mutagen and screening survivors for increased titers of the enzyme. This method, as practiced in the prior art, has the disadvantage of being long and tedious because of the time and effort required to select the fungi that create the higher titer of the enzyme.
Another prior art process for selecting and growing mutants of fungus is described in U.S. Pat. No. 4,115,197. This patent describes a process in which the mutants are selected through the use of an antibiotic to which the mutants are resistant. This prior art process has the disadvantages of: (1) requiring antibiotics and a further separation step; and (2) generally not selecting for unrelated metabolites.
It is also known to detect mutants by the change in pH caused by action of an enzyme on a substrate. This prior art teaches the use of pH detectors that indicate pH conditions of 5 or 6. These pH detectors are not suitable for detection of enzymes that change acidity in the already acid substrate of Aspergillus niger.